In a technique that has been proposed recently, an operation status of a network is monitored by an NMS (Network Management System) or a local control terminal which utilizes an SNMP (Simple Network Management Protocol) (see, for example, Patent Document 1).
A communication device that is a target to be monitored in the above-described manner discloses setting information or operating information of the present device by means of an MIB (Management Information Base) that is a database for managing devices in a communication network.
The NMS or the local control terminal acquires information, that is published by the MIB, via the relevant network.
For example, when monitoring a network status of a VLAN (Virtual Local Area Network) utilizing an SNMP, generally, a standard MIB defined in “RFC 2674” or the like or an extended MIB provided by an individual device vendor is utilized.
FIG. 5 is a diagram that shows a VLAN data structure of the standard MIB defined in RFC (Request for Comments) 2674.
In the standard MIB (dot1qVlanCurrentTable) that defines each status of VLANs, each port in each VLAN is managed by the bit. In the example of FIG. 5, VLAN management data 930 of each VLAN is stored in the MIB.
The VLAN management data 930 includes group data items 940, each of which is one-byte (octet string) data. Each group data item 940 contains eight individual data items 950. Each individual data item 950 indicates the status of one target port by 1 bit.
For example, if the relevant port is active (currently used) in the VLAN, the individual data item 950 has a value of “1”. In contrast, if the relevant port is not active in the VLAN, the individual data item 950 has a value of “0”.
According to such a structure, in the standard MIB, the amount data is increased by the byte (corresponding to eight ports).
As described above, in the standard MIB defined in RFC 2674, the status of each port is managed for each VLAN. Therefore, in order to check the states of VLANs, a “Get Request” message of SNMP is sent, for each VLAN, from the NMS to the relevant communication device so as to obtain the VLAN management data 930. Accordingly, the number of “Get Request” messages sent from the NMS to the communication device increases according to an increase in the number of VLANs registered with the communication device.